1. Field of the Invention
This invention relates generally to data processing systems, and more particularly to data processing systems capable of processing data under control of a plurality of operating systems. Typically, however, each operating system has different addressing mechanisms as well as different attributes associated with the data fields of the operating system. The attributes and parts of the addressing mechanisms are included in data fields referred to as descriptors.
2. Description of Related Art
It is known in the related art to utilize separate apparatus with each operating system of a data processing system. The necessity for separate apparatus was a result of the diverse manner in which each operating system can handle the address formation and the attributes associated with an operating system. Typically, each operating system will have a different descriptor format for providing address data and the associated attributes. As a result, even improvements in operating systems programs were constrained to function within the available apparatus, thereby severely limiting the possible alterations.
A significant problem results from the use of the descriptors. Descriptors are groups of data associated with the execution of instructions by the central processing unit. The descriptors typically include information necessary for address formation, but also include additional information about the data signal groups. The additional information can be unique to a particular operating system or it can be general in nature. For example, in the Multics operating system, the ring identification number can determine the user access to data and consequently must be retained whenever instructions in the Multics operating systen repetoire are executed.
Therefore a need has been present for a central processing unit which is able to utilize a plurality of descriptor formats without apparatus individualized to each of the operating systems. The central processing unit can, with additional modifications, be capable of control by a plurality of operating systems.